Impact fuse

ABSTRACT

The invention relates to an impact fuse comprising a body containing a piezoelectric generator put in place on a bracket integral with the body and forming an anvil, said fuse comprising a piston intended to come to exert a mechanical stress on the generator, said piston receiving the impact strain transmitted by a cap, said fuse being wherein the piston is slidably fitted relatively to the body and in that it comprises plastically deformable means that are interposed between the cap and the body, said means being deformed by the cap movement on impact on a target, said movement causing a piston movement, the energy consumed by the means deformation thus allowing to ensure a longer and more gradual crushing of the piezoelectric generator on impact on a target.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The technical field of the invention is that of impact fuses for projectiles.

2. Description of the Related Art

It is known to create impact fuses including a piezoelectric generator that generates an electrical voltage on impact of the fuse on a target.

Most of the time, the piezoelectric generators are constituted by one or several piezoelectric ceramics stacked on one another. Such a generator is put in place on a bracket that is integral with the fuse body and forms an anvil at the time of the shock.

In other respects, the fuse comprises a piston that comes to exert a mechanical stress on the generator on impact. The FR-1595412 patent describes such a known impact fuse. The electrical voltage obtained is used to initiate an electrical primer.

One of the problems met with the known fuses is that, under some impact configurations, the electrical voltage generated may happen to be insufficient to ensure the initiation of the primer.

This is due to the fact that the shock received by the generator is too brief.

In other respects, it is needed to ensure the integrity of these fuses by avoiding that an impact of a given relatively low energy level generates a deterioration of the casing that might disturb the reliability.

The constraints met are thus relatively contradictory. On the one hand, it is needed to allow a deformation of the generator sufficient to ensure a nominal electrical voltage allowing the initiation of the primer. On the other hand, it is needed to prevent any deformation of the generator at the time of a reduced level shock.

The FR-2669416 patent describes a priming device that comprises a piezoelectric generator integral with the fuse body and is actuated by a hammer on impact on a target. Thus, the hammer is projected toward the piezoelectric generator at the time of a shock on the fuse cap. With such a concept, the shock received by the generator is all the same too brief.

In other respects, the WO-85/03345 patent describes a percussion fuse comprising a piezoelectric generator and some means allowing to enhance the safety of use. These latter means combine a self induction coil and a spark gap. Thus the firing is caused only when the rising edge of the received pulse exceeds a given amplitude.

The purpose sought for by this patent is different than that aimed at by the invention since here the purpose is to create a mechanical link ensuring a high and brief pulse of the piston on the crystal.

SUMMARY OF THE INVENTION

It is the purpose of the invention to provide an impact fuse with a piezoelectric generator having enhanced initiation reliability and providing an optimal safety of use all the while.

Thus, the invention relates to an impact fuse comprising a body containing a piezoelectric generator put in place on a bracket integral with the body and forming an anvil, said fuse comprising a piston intended to come to exert a mechanical stress on the generator, said piston receiving the impact strain transmitted by a cap, said fuse being characterized in that the piston is slidably fitted relatively to the body and in that it comprises plastically deformable means that are interposed between the cap and the body, said means being deformed by the cap movement on impact on a target, said movement causing a piston movement, the energy consumed by the means deformation thus allowing to ensure a longer and more gradual crushing of the piezoelectric generator on impact on a target.

The plastically deformable means may be constituted by a metal washer comprising at least one deformable rim. The metal washer may comprise at least two rims separated by a groove. In other respects, the washer may be implemented of aluminum or aluminum alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become better understood from the following description of a particular embodiment, with reference to the accompanying drawings, wherein:

FIG. 1 is a diagrammatic longitudinal cross-sectional view of a fuse according to an embodiment of the invention,

FIG. 2 is a front view of the washer implemented in this fuse.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a head fuse 1 for a projectile. This fuse is intended to be put in place at the level of a front end of a projectile (not shown), for example an artillery or tank shell or a mortar projectile.

The fuse 1 comprises a body 2 having a threaded rear part 2 a, which may be screwed to the projectile, and a truncated cone-shaped front part 2 b. The rear part 2 b contains an electronic circuit 3 that is connected on one side to a piezoelectric generator 4 and on the other to a primer 5.

This electronic circuit does not constitute the object of the present invention and so will not be further described.

The piezoelectric generator 4 is put in place in a housing 6 arranged at an end of the rear part 2 a of the body 2. The rear part 2 a of the body 2 thus constitutes an anvil-forming bracket.

The fuse 1 comprises a piston 7 that is slidably fitted into an axial bore 8 of the front part 2 b of the body 2.

The piston 7 is intended to come to exert a mechanical stress on the generator 4 and so comprises a face bearing on this generator.

The piston 7 is made integral (for example, by screwing) with a cap 9 that extends the front part 2 b of the fuse body. On impact on a target, the cap 9 transmits a strain to the piston 7 that in turn conveys it to the piezoelectric generator 4. In other respects, the piston is partly immobilized against translatory motions by a slit elastic ring 13 provided in a peripheral groove of the piston. This ring 13 avoids any extraction of the piston 7 out of its housing. On the other hand, it does not prevent the piston 7 from moving toward the generator 4. A ledge arranged on the piston 7 could replace the ring 13.

According to the invention, the fuse comprises some plastically deformable means that are interposed between the cap 9 and the body 2. Those means are constituted by a metal washer 10 (made of aluminum or aluminum alloy) comprising at least one deformable rim 11. As may be more clearly seen from FIG. 2, the rims 11 are separated by circular grooves 12.

The washer material is chosen so that it is plastically deformable at the time of a shock on a target. This means that the washer deformation is irreversible.

Are thus excluded to implement the washer 10 the plastic materials or the materials that stay (under the shock conditions on a target) in an elastic deformation domain.

Those skilled in the art shall thus size the rims 11 (number and thickness) according to the operational constraints met. In other respects, the washer 10 stiffness ensures the piston 7 immobilization during the stocking stages or at the times of falls.

The rims 11 are sized so that they crushed only on impact on a target after an effective firing of the projectile. The energy consumed by the washer 10 deformation allows to ensure a longer and more gradual crushing of the piezoelectric generator 4. The result of this is a higher electric voltage and a better initiation reliability.

Various alternative embodiments may be designed without departing from the scope of the invention.

The washer 10 axial position relatively to the body 2 may thus be varied. It shall be noted that the more the washer 10 is in the rear, the more the fuse is sensitive at the time of a grazing impact. In other respects, a conical interface may be provided between the piston 7 and the cap 9 (as described by the patent FR1595412).

An annular piston 7 may as well be implemented (cooperating with an also annular piezoelectric generator) to allow for example the putting into place of operation mode programming means at the fuse axis level. 

1. Impact fuse comprising a body containing a piezoelectric generator put in place on a bracket integral with said body and forming an anvil, said fuse comprising a piston intended to come to exert a mechanical stress on generator, said piston receiving the impact strain transmitted by a cap, wherein said piston is slidably fitted relatively to said body and wherein said fuse comprises plastically deformable means that are interposed between said cap and said body, said means being deformed by the movement of said cap on impact on a target, said movement causing a movement of said piston, the energy consumed by the deformation of said deformable means thus allowing to ensure a longer and more gradual crushing of said piezoelectric generator on impact on said target.
 2. Impact fuse according to claim 1, wherein said plastically deformable means are constituted by a metal washer comprising at least one deformable rim.
 3. Impact fuse according to claim 2, wherein said metal washer comprises at least two rims separated by a groove.
 4. Impact fuse according to claim 2, wherein said washer is implemented of aluminum or aluminum alloy. 